1. Field of the Invention
The present invention relates to a transfer device for use in an electrostatic photo-processing (image-forming system) such as in an electrostatic copying machine, a printer, a facsimile and the like. More specifically, the invention relates to a transfer device which prevents the organic photosensitive material from being deteriorated by the use of a transfer roller.
2. Description of the Prior Art
In an image-forming apparatus based upon the electrostatic photo-processing, the toner image formed on an image carrier is transferred by passing a transfer material such as a paper between the image carrier and a transfer roller that is disposed being opposed thereto.
Japanese Laid-Open Patent Publication No. 77063/1989 discloses a transfer roller having a hardness of 30.degree. (JIS A) or smaller that is employed for such a transfer device. That is, this transfer device uses a transfer roller of a low hardness to prevent the coagulation of the toner that exists on the surface of the image carrier and to facilitate the cleaning with ease.
Moreover, Japanese Laid-Open Patent Publication No. 200277/1989 discloses a transfer system using the same transfer roller as the one described above or a like transfer roller wherein an electric charge of a polarity opposite to that of the toner is fed to a transfer material in a state where there exists a gap with respect to the image carrier (photosensitive material) and, then, the transfer material is brought into contact with the image carrier.
It was found, however, that the organic photosensitive material is deteriorated when the transfer system using the above-mentioned transfer roller is adapted to the organic photosensitive material that contains a charge-generating agent and a charge-transporting agent.
That is, the transfer roller made of an electrically conducting polyurethane rubber composition exhibits excellent abrasion resistance, electric properties and ozone resistant properties. When this transfer roller is used for transferring the toner from the organic photosensitive material onto the transfer material, however, image defects such as white spots and the like occur due to deterioration of the organic photosensitive material.